This invention relates to ultrasonic monitoring systems and methods and, more particularly, ultrasonic systems mounted on pipes for monitoring valve conditions.
Non-intrusive online monitoring of valves, such as check valves, has acquired a great importance in many industrial applications. In the nuclear industry, check valves and other comparable valves, though simple in function, are critical to safe plant operation. In fact, such valves are subject to NRC-specified periodic inspections that, in the past, have usually required time-consuming and expensive partial disassembly. Although systems are available for monitoring motor-operated valves, there remains a need for a reliable system for monitoring check valves and the like which would avoid disassembly and consequent down time.
In the past, there have been a number of check valve diagnostic methods developed and marketed, but each is characterized by certain limitations and disadvantages. Ultrasonic systems have been proposed for directly monitoring valves, by using external transducers in the pulse-echo or through-transmission modes. However, in attempting to mount external transducers on valve parts, difficulty is encountered in obtaining desired acoustic paths and good acoustic coupling, because of the non-uniform makes and styles of valves and the consequent differing geometries and exterior surface finishes.
An acoustic technique, commonly referred to as Acoustic Emission (AE), has been used in many different monitoring applications. In this method, external transducers mounted on a valve and operating in a passive listening mode respond to acoustic energy in the metal which results from impacts and/or vibrations of valve parts. In other words, the transducer acts only in a listening, or receiving mode, to pick up acoustic signals generated by the valve. However, such transducers are sensitive to unwanted vibration and noise pick-up, and the resulting acoustic signals are difficult to interpret.
Another approach makes use of a permanent magnet installed on a moving valve part, with means for sensing the position of the moving magnet by an external magnetic sensor. This method is limited in that it requires modification of the valve to install a magnet, and may not be useful in many applications, e.g., those involving carbon steel valves. In yet another approach, x-rays have been used to show the position and possibly the condition of internal parts of valves. However, the x-ray approach involves large, expensive equipment, and also generates safety concerns.
There thus remains a very practical commercial need for an improved monitoring system and method, particularly for check valves in a nuclear power plant environment. Although this invention is illustrated by showing the swing-type of check valve, which is the most common, it is to be understood that other types of check valves and similar valves are within the scope of the invention.